This invention relates to unique holographic films, and in particular to unique holographic films that receive a holographic image, in the form of an embossed image, that is imparted to a subsequently applied metallized layer. In the preferred embodiments of the invention the metallized layer is a permanent layer of the film, and in other embodiments the metallized layer is transferable from the film to another substrate.
Holographic films including metallized layers are known in the art, and are utilized for a wide variety of applications, e.g., flexible packaging substrates for food products, gift wrapping paper, and as a decorative component in non-flexible packages or rigid packages, e.g., packages for tubes of toothpaste, cereal boxes, detergent boxes, etc. For many applications, and in particular in the packaging of food products, it is desirable that these metallized films have good oxygen and moisture barrier properties.
An exemplary, commercially available transparent holographic film includes a Ziegler-Natta catalyzed propylene-ethylene copolymer (3-7% ethylene) outer layer for receiving an embossed holographic pattern therein. The gloss of this film, prior to receiving the metallized layer thereon, is approximately 110 units when measured at a 20xc2x0 angle employing ASTM D2457-97. Although an outer layer formed of 100% Ziegler-Natta catalyzed or metallocene catalyzed isotactic polypropylene homopolymer has the desired gloss (e.g., on the order of 135 to 140 gloss units as measured at a 20xc2x0 angle employing ASTM D2457-97) this polymer has a melting point that is too high to permit its effective use in the holographic films of this invention.
The art of transferring a holographic image from one substrate to another also is known, as is disclosed in copending application Ser. No. 09/627,977, filed on Jul. 28, 2000, now U.S. Pat. No. 6,558,788 B1 titled Holographic Transfer Films and identifying Michael D. Butler and Shailesh Chunilal Patel as joint inventors. In addition holographic transfer films for receiving a metallized layer thereon for subsequent transfer to another substrate are known in the art, as exemplified in U.S. Pat. Nos. 5,662,986; 5,735,989; 5,723,203; 5,746,865; 5,766,734; 5,871,608; 5,900,095 and 5,902,436. The subject matter of the above-identified ""977 application and of all of the above-identified patents is incorporated herein by reference.
While holographic films presently are commercially available, a need exists for improved holographic films having a metallized layer with enhanced brightness and sharper and crisper holographic images therein. It is to such holographic films that the present invention relates.
The above and other objects of this invention are achieved in a multilayer (e.g., two or more layers) holographic film including a core layer, preferably comprising polypropylene, and at least one hologram-receiving layer on at least one side of said core layer, and preferably adhered to at least one surface of the core layer for including an embossed, holographic image therein and being adapted to receive a metal layer thereon, said hologram-receiving layer(s) comprising a butene-propylene random copolymer having a melting point in the range of between about 125xc2x0 C. and about 145xc2x0 C. Most preferably an embossed, holographic image is provided in the hologram-receiving layer(s) and a metal layer is provided on the embossed hologram-receiving layer(s) so as to include an image therein conforming to the embossed holographic image in said hologram-receiving layer(s).
Although it is within the scope of this invention to provide hologram-receiving layers on opposed sides of the core layer, in the most preferred embodiments of the invention a hologram-receiving layer is provided on only one side of a core layer of the multilayer films. Therefore, throughout the remainder of this specification, the most preferred multilayer films of this invention will be described, wherein only a single hologram-receiving layer is provided. However, it should be understood that within the broadest aspects of this invention, each of the disclosed hologram-receiving layers can be on opposed sides of the core of the multilayer film.
In a preferred embodiment of the invention, the hologram-receiving layer comprises at least about 25%, by weight, of a butene-propylene random copolymer containing more than 8%, by weight butene therein.
In another preferred embodiment of the invention the hologram-receiving layer comprises at least about 50%, by weight, of a butene-propylene random copolymer containing more than 8%, by weight butene therein.
In another preferred embodiment of the invention the hologram-receiving layer comprises substantially 100%, by weight, of a butene-propylene random copolymer containing more than 8%, by weight butene therein.
Most preferably the butene-propylene random copolymer employed in this invention includes a percentage of butene, by weight, in the range of about 8% to about 16%. Most preferably the percentage of butene, by weight, is about 14%.
In the preferred embodiments of this invention, the thickness of the hologram-receiving layer should be greater than the depth of the embossed holographic image. Preferably the thickness should be at least 2 gauge; more preferably in the range of 2 gauge to 8 gauge; even more preferably in the range of 4 gauge to 8 gauge and most preferably approximately 6.5 gauge.
In accordance with certain preferred embodiments of the invention, said hologram-receiving layer includes a metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% blended with a butene-propylene random copolymer containing more than 8%, by weight butene therein.
In accordance with certain preferred embodiments of the invention, the hologram-receiving layer includes approximately 50%, by weight, of the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% and approximately 50%, by weight, of the butene-propylene random copolymer containing more than 8%, by weight butene therein.
In accordance with certain preferred embodiments of the invention the hologram-receiving layer includes a metallocene catalyzed, isotactic C3 homopolymer blended with a butene-propylene random copolymer containing more than 8%, by weight, butene therein. In certain embodiments the metallocene catalyzed, isotactic C3 homopolymer constitutes approximately 50%, by weight, of the blend and said butene-propylene random copolymer containing more than 8%, by weight butene therein constitutes approximately 50%, by weight of the blend.
In certain preferred embodiments of the invention the hologram-receiving layer includes a metallocene catalyzed, isotactic C3 homopolymer blended with a metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% and with a butene-propylene random copolymer containing more than 8%, by weight butene therein. In certain preferred embodiments the metallocene catalyzed, isotactic C3 homopolymer constitutes approximately 50%, by weight, of the blend, the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% constitutes approximately 25%, by weight of the blend and the butene-propylene random copolymer containing more than 8%, by weight butene therein constitutes approximately 25%, by weight of the blend.
In accordance with another embodiment of this invention a multilayer holographic film includes a core layer comprising polypropylene and a hologram-receiving layer adhered to one surface of the core layer for including an embossed, holographic image therein and being adapted to receive a metal layer thereon, said hologram-receiving layer comprising a metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% having a melting point in the range of between about 120xc2x0 C. and about 140xc2x0 C. Most preferably the hologram-receiving layer includes an embossed, holographic image therein and a metal layer on the embossed hologram-receiving layer includes an image therein conforming to the embossed holographic image in said hologram-receiving layer.
In a preferred embodiment of the invention, the hologram-receiving layer comprises at least about 25%, by weight, of the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2%.
In another preferred embodiment of the invention, the hologram-receiving layer comprises at least about 50%, by weight, of the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2%.
In another preferred embodiment of the invention, the hologram-receiving layer comprises substantially 100%, by weight, of the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2%.
In another preferred embodiment of the invention the hologram-receiving layer includes a metallocene catalyzed, isotactic C3 homopolymer blended with a metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2%. In one preferred embodiment the metallocene catalyzed, isotactic C3 homopolymer constitutes approximately 50%, by weight, of the blend and the metallocene catalyzed, isotactic C2/C3 random copolymer with a C2 content of at least about 2% constitutes approximately 50%, by weight of the blend.
In accordance with all embodiments of the invention the thickness of the hologram-receiving layer is at least 2 gauge; more preferably in the range of 2 gauge to 8 gauge; even more preferably in the range of 4 gauge to 8 gauge and most preferably approximately 6.5 gauge.
In accordance with another embodiment of the invention, a multilayer holographic film includes a core layer comprising polypropylene and a hologram-receiving layer adhered to one surface of the core layer for including an embossed, holographic image therein and being adapted to receive a metal layer thereon, said hologram-receiving layer being untreated and comprising a high density polyethylene having a melting point in the range of between about 120xc2x0 C. and about 135xc2x0 C. Reference throughout this application to xe2x80x9chigh density polyethylenexe2x80x9d refers to a polymer having a density of at least 0.935 gms/cc. Most preferably an embossed, holographic image is provided in the hologram-receiving layer and a metal layer on the embossed hologram-receiving layer includes an image therein conforming to the embossed holographic image in said hologram-receiving layer.
In certain embodiments of the invention the high density polyethylene constitutes in excess of 40%, by weight, of the hologram-receiving layer.
In certain embodiments of the invention, the high density polyethylene constitutes at least 50%, by weight, of the hologram-receiving layer.
In certain embodiments of the invention the high density polyethylene constitutes approximately 100%, by weight, of the hologram-receiving layer.
In accordance with the broadest aspect of this invention, the high density polyethylene can be either a homopolymer or a copolymer.
In certain embodiments of the invention a terpolymer of ethylene-propylene-diene monomer is blended with said high density polyethylene in the hologram-receiving layer. In certain preferred embodiments the high density polyethylene and the terpolymer are present in substantially equal weight percentages.
In all embodiments of this invention the film can include a slip layer adhered to the surface of the core opposite the surface to which the hologram-receiving layer is attached. Preferably the slip layer includes predominantly a polypropylene homopolymer and a substantially non-migratory slip agent in said homopolymer. A preferred slip agent for use in the invention is a cross-linked silicone present in an amount of no more than 2500 ppm.
In all embodiments of the invention it is preferred that the film be substantially free of migratory ingredients and also free of additives that degrade the embossed, holographic image.
In the preferred embodiments of the invention the core layer is polypropylene, and most preferably is a member selected from the group of metallocene catalyzed isotactic polypropylene homopolymers, Ziegler-Natta catalyzed isotactic polypropylene homopolymers, propylene/ethylene random copolymers (either Ziegler-Natta or metallocene catalyzed), high crystalline polypropylene homopolymers, blends of two or more of said homopolymers and syndiotactic polypropylene homopolymers blended with one or more of said other homopolymers. Although, the specific composition of the core does not constitute a limitation on the broadest aspects of this invention, the core needs to have a melting point higher than the hologram-receiving skin layer.
In all embodiments of the invention the film includes in excess of 115 gloss units, prior to metallization, as determined by ASTMD2457-97 at an angle of 20xc2x0. More preferably the film includes at least about 135 gloss units, prior to metallization, as measured by ASTMD2457-97 at an angle of 20xc2x0.